UACES Facebook Preflood Nitrogen in Rice: Core Principles for Nitrogen Efficiency and Yield Protection
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Preflood Nitrogen in Rice: Core Principles for Nitrogen Efficiency and Yield Protection

by Ana Smith, assistant professor and extension soil fertility specialist; Justin Chlapecka, assistant professor and research agronomist; and Trent Roberts, professor and extension soil fertility specialist, Department of Crop, Soil and Environmental Science, University of Arkansas Division of Agriculture - May 26, 2026

Preflood nitrogen (N) is the most important fertilizer decision for Arkansas rice producers. This application typically accounts for 65% to 100% of the season total N rate and is the primary engine that determines overall yield potential. Preflood N is responsible for setting two of the three primary yield components in rice, and its proper management is tied directly to rough rice and milling yield. Below, we review the core principles of preflood N management, including timing, flood establishment, and practices that help maximize N efficiency and protect yield.

Hit the timing and apply to dry soil

Preflood N should be applied to dry soil immediately prior to flooding, ideally near the 4- to 5-leaf growth stage. At this stage, the rice is beginning to tiller, and its demand for nutrients is about to skyrocket. Additionally, the sooner a flood is established, the sooner we can suppress weed emergence.

Applying N to dry soil is critical for efficiency. When urea is applied to a dry surface and then flooded, the water moves the N into the soil where it is protected from surface-based losses (ammonia volatilization). Research shows that N applied immediately before the flood results in the highest yields and greatest fertilizer use efficiency.

Use DD50 to guide application timing

Because every cultivar develops at a different speed, there is no single calendar date that works for every field. Instead, growers should rely on the DD50 Rice Management Program (https://dd50.uada.edu/).

The DD50 printout provides a specific window of dates (usually a couple of weeks) tailored to your specific cultivar and emergence date. Specifically, the program targets the window when 350 to 550 heat units have accumulated (approximately the 4- to 5-leaf stage), marking the optimal time to stimulate tiller formation and help maximize the first rice yield component, which is panicles per acre.

Please remember that DD50 growth stage predictions are based on 30-year weather data and that deviations in daily temperature can speed up rice growth and development (daily temperatures higher than average) or slow down growth and development (daily temperatures that are cooler than average). It is strongly suggested that DD50 reports are updated at various points in the growing season to account for current season temperature fluctuations that may lead to rice moving faster or slower than predicted at emergence. The DD50 will provide an optimal window for preflood N application and a final recommended time to apply preflood N. The final recommended time to apply preflood N is roughly three weeks prior to ½ inch internode elongation and is the point where rice yield may suffer without N application. For reference in an average weather year, rice that emerged on the second week of April in Poinsett County will be approaching the final recommended time to apply preflood N by May 20. Rice that emerged during the third week of April is closer to the first week of June for final recommended preflood N timing.

Fix deficiencies early

One of the costliest mistakes a grower can make is waiting for a midseason application to correct an early-season problem. If your rice becomes yellow or shows signs of N deficiency during the vegetative growth stage, you must act immediately.

Apply enough N to correct the deficiency (100 lb urea/acre) immediately. Never wait until midseason to fix a vegetative N deficiency. By that point, the number of panicles and grains per panicle have already been set, and the lost yield potential cannot be fully recovered.

Adjust for muddy conditions

We know Arkansas weather doesn't always cooperate. While every effort should be made to apply N to dry soil, wet conditions can sometimes persist through your entire DD50 window.

If you cannot wait for the soil to dry, use NBPT-treated urea on the muddy soil, but wait for the surface to dry before establishing the flood to reduce N loss risk. The two issues with muddy soil are that 1) it increases ammonia volatilization loss potential (can be mitigated with NBPT) and 2) when the soil is muddy the urea cannot incorporate or move into the soil profile. Oftentimes if we apply urea and flood before the soil is dry the urea dissolves into the flood water and does not move into the soil which leads to N losses and potential yield losses. As a general rule of thumb, once the soil starts to “whitecap” you can safely apply the flood and effectively incorporate the urea into the soil.

Seasonal updates and additional guidance

While the core principles of preflood N management remain consistent, weather and season-specific conditions may require additional considerations related to stand establishment, muddy soils, delayed flooding, and other in-season challenges. For season-specific recommendations and updates, including adjustments for low stands and difficult field conditions, see the latest Arkansas Rice Updates from Dr. Jarrod Hardke, Rice Extension Agronomist.

Key Takeaway:

Your preflood N determines your yield potential. Use DD50 to time the 4-to-5 leaf stage, apply on dry soil, use NBPT when appropriate, and fix N deficiencies immediately to protect your yield.

References:

https://www.uaex.uada.edu/farm-ranch/crops-commercial-horticulture/rice/Rice-Management-Guide.pdf

https://www.uaex.uada.edu/publications/pdf/mp192/chapter-9.pdf

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